One of the control techniques of supercharged engines which attracts attention at present is active control of a waste gate valve using an electric actuator such as an E-VRV (Electronic Vacuum Regulating Valve). In the active control, a waste gate valve is moved to an optional opening according to a manipulation signal from an ECU, and thereby, a turbo rotational speed is actively controlled. According to this, a supercharging pressure can be optionally regulated, and further improvement in fuel economy performance and exhaust gas performance is achieved.
However, in order to achieve such active control, it is necessary to understand how much the waste gate valve is actually opened. This is because even when the waste gate valve is actively operated, if the opening thereof deviates from an originally-planned opening, the engine experiences troubled operation. For example, if the waste gate valve is closed more than planned in a heavy load state, pre-ignition occurs due to excessive supercharging. Conversely, if the waste gate valve is opened more than planned, desired acceleration performance cannot be obtained due to an insufficient supercharging pressure. Further, information about a waste gate valve opening is important for accurately estimating air quantity in a cylinder.
However, it is not easy in realty to measure a waste gate valve opening with high precision by measuring means such as a sensor. Accordingly, if information about a waste gate valve opening is necessary, the waste gate valve opening must be estimated from a manipulated variable at a time of an ECU manipulating the waste gate valve. More specifically, the waste gate valve opening is estimated from the manipulated variable of the waste gate valve by using a correspondence relation that is defined in advance. However, a deviation is likely to occur between an actual correspondence relation and the defined correspondence relation due to an individual difference and aged deterioration of the waste gate valve. In such a case, the estimated value of the waste gate valve opening differs from the actual value, and engine control is adversely affected when engine control is performed with reference to the estimated value of the waste gate valve opening. Because of this, when active control of a waste gate valve is carried out, the technique capable of obtaining an accurate estimated value of the waste gate valve opening is also required.
As prior art relating to the present invention, the following prior art described in respective Patent Documents is cited. For example, Japanese Patent Laid-Open No. 2004-156525 indicates that the valve lift amount which is the cause of an error is corrected based on an error between an actual intake valve flow rate and an estimated intake valve flow rate which is calculated by using a model. However, Japanese Patent Laid-Open No. 2004-156525 does not mention a waste gate valve, to say nothing of describing the method for obtaining an accurate estimated value of a waste gate valve opening.